The extremists Saturday stole relics, historic books and manuscripts that were inside one of the religious sanctuaries in Mosul, Iraq's second-largest city, before demolishing the buildings with large earthmoving machines.

In addition to razing several sanctuaries, they destroyed the mosque of Muhsin, from which they stole valuable objects that had been housed there.

The government source said the jihadis demolished that site, which consisted of a small 5th-century mosque with a large cupola and contained one of the tombs of the imam Muhsin.

The IS, meanwhile, released a video showing the group's destruction of mosques and religious sites, calling it a "fight against ... heresy.

"The IS practices an extreme version of Sunni Islam that rejects the existence of mausoleums inside mosques because it feels that then the faithful could potentially direct their prayers to the dead resting there rather than to God.

Meanwhile, Iraqi security forces recovered control of most of the city of Biyi, 40 km north of Tikrit, capital of Saladin province, Governor Jasem al-Jabara said.

Iraqi troops, aided by tribal fighters, retook the city's industrial zones, the military district, the market area, the railroad sector and all the neighbourhoods near the Biyi refinery, along with other sections of the city.

They also advanced toward Al Siniya, 10 km west of Biyi, where they retook control of the region's oil refinery in clashes with occupying jihadis that resulted in dozens of dead and injured in the IS ranks.

Iraqi authorities last November had announced their intention to regain control of strategically important Biyi, although the IS had made significant advances in the area and took over parts of the city on December 21 after a series of attacks on government positions.

Biyi is the site of Iraq's largest oil refinery -- which produces 250,000 barrels of crude per day, although it was shut down June 10, 2014, after jihadis advances in the area -- and a hub for supply routes to Nineveh, Al Anbar and Kirkuk provinces.

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